TRANSMISSION IS NOT SHIFTING INTO OVERDRIVE SOMETIMES

1997 GMC Sierra

Rebuilt Trany 4L60E Scanner Code P1860 - will shift to overdrive sometimes need help with code to fix overdrive problem Joe rebuilt the transmission at work on 97 Sierra 4WDR 4L60E transmission. He drove it and it will shift to overdrive sometimes then sometimes it will not. Ran scanner test and the code comes back to P1860. Checked for fuse or bad ground and found nothing. Can you please help with this so he can fix the work truck and come home for X-Mas Vacation. Thanks and Merry Christmas to you and your families.

Did you send me a email on this site or to my personal yahoo email?Its actually better we back and fourth on this question right hear. Other users use this questions to help them fix there own issues there having with there vechiles.

OK, he has cleared the code 3 times. Drove it and what happens is it shifts to overdrive with scanner hooked up. When he stops at a light and the trany shifts to 1st. Then light comes back on and scanner code reads the same P1860. I was told to get a computer, which a guy has one for $50. And have the vin# programed in it and then it will really clear the code out. What do you recommend.

No thats not what I ment. Sorry if I confused you. He cleared it while he was driving and then it would read the code again when he stopped at a light. He cleared it six times that way and it has stopped, so we think. The main guy that drives it is taking it home tonight to see if the light stays off. After clearing it so many times it seems to be working. My question is, if the light comes back on again in the AM and the scanner code reads the same P1860 code, will it basically mean the PCM (like a PC virus I think) may be stuck in reading that code from before he changed the trany. He has already put a new TCC solenoid & shift timing solenoid. Do you recommend the new computer to finally clear up all the codes. Does the computer have to be vin coded if the key isn't key coded? He said no, but the guy I talked to said it did. Thanks for all your help.

Wow, clearing the code does nothing. The problem is there and will continue to be there till it is identified and repaired. You need to look at the freeze frame data when the light comes on to see what reading is not correct. The pcm is the last thing to replace before checking all the solenoids and wiring. Used computers are bad ideas as well. It could make things worse.

Have a trans shop look at it for you. Do not clear the code and let them see the freeze frame data.